For Democrats Abroad, the biggest contest in years

The constituency is thousands of miles wide and contains around six million voters with a keen interest in the primaries but you won't find a reference to it on a map of the United States. It is the constituency of Americans abroad and last night they were voting in their hundreds of thousands from Tokyo to Berlin and from central Jakarta to chilly Paddington.

"I've never seen so much activity," said Daniel Rivkin of Democrats Abroad UK before voting started at Porchester Hall in central London, which had been hired for the occasion. "Our membership has doubled in the last month. We have two great candidates whose supporters are very passionate and people feel that anything could happen. It reflects what is happening in the United States."

Rivkin said a new president could help to improve relations between the US and the rest of the world which had been damaged by the Iraq war.

Rivkin, who has lived abroad for 17 years in Paris, Brussels and London, where he has worked until recently for Reuters, said the interest this year was unprecedented in his experience and he was expecting a record turnout.

"It is a historic election," agreed Bill Bernard, the chairman of Democrats Abroad UK, who lives in Oxford, where people will also be able to vote. He also has never seen such interest in the outcome.

At Porchester Hall dozens of supporters of Hillary Clinton and Barack Obama were gathered outside wearing campaign T-shirts and carrying placards. Inside was a sea of red, white and blue. A Clinton supporter, Ellen McCoy from Washington DC, said: "There has been a huge effort to get the vote out. This time we've got to get a Democrat elected."

Karin Robinson who has lived in England for nine years, said she was backing Obama and that there was much more interest in the primaries than before.

"This is a million miles from where we were four years ago," she said. "We would like the country to be led by Democrats'

Democrats Abroad has committees throughout Europe, the Americas, the Middle East, Africa, Asia, and the antipodes and is recognised as a "state" party. It will have 22 delegates at the party's convention in Denver in August and was host to 76 voting events in 33 countries last night. Organisers estimated that voter participation had increased around seven-fold from the rather lacklustre primaries in 2004, which heralded a disastrous showing by the Democrats in the November election.

In London, Republicans Abroad have a different set-up from the Democrats and were not casting ballots. They gathered instead at Henry's in Covent Garden for a social evening.

"We have supporters of both [Mitt] Romney and [John] McCain," said Miki Bowman, who chairs Republicans Abroad. She said that they were conducting an online straw poll to see how their members intended to vote.

The United Kingdom has one of the largest concentrations of Americans abroad - an estimated 250,000 to 300,000. Both parties value their support, not least as fundraising bases.

The first of the American expats to participate voted at a hotel in Jakarta. Throughout the day and night countless others were dropping their ballots in or watching events unfold on television in bars and pubs from Dublin to Sydney. Jakarta sent Obama into an early lead, if only for a few minutes, with around 75% of the first 100 votes cast, three times what Clinton was receiving.

In Bangkok Americans headed to the Foreign Correspondents' Club of Thailand to register their votes. In Dublin Democrats Abroad had installed themselves in O'Neills pub.